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SubjectRe: 2f47e7e19f ("x86/mm/kaiser: Use PCID feature to make user and .."): WARNING: CPU: 0 PID: 1 at mm/early_ioremap.c:114 __early_ioremap
Hello Dave,

On Mon, Nov 27, 2017 at 06:51:12AM -0800, Dave Hansen wrote:
> On 11/27/2017 02:18 AM, Ingo Molnar wrote:
> > Any ideas about this bug?
> I suspect that it's not bisected perfectly. I did some testing with
> that config and it pretty much boots or crashes randomly.
> Booting in a VM on a CPU without PCID support gets crashes in early
> userspace, which has tended to be a TLB flushing problem. I'll narrow
> it down some more today.

On top of VM crashes, on your branch:

I am also getting crashes in early userspace, during tlb flushes. When KAISER is enabled and whenever userspace is loaded, I get a stack trace around __do_page_fault() called from restore_regs_and_return_to_kernel(). I saw this very same behavior in your v3 branch (kaiser-414-tipwip-20171121) too.

The crashes are followed by a machine halt via NMI. They also get the following warning:
WARNING: can't dereference iret registers at fffffffffe198048 for ip page_fault+0x11/0x60

I see this behavior on my laptop:
Model name: Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt xsaveopt xsavec xgetbv1 dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp

All the best,
Eduardo Valentin

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